Circumnavigator on staff discovers magical plant (8)
I believe the answer is:
mandrake
'plant' is the definition.
(mandrake is a kind of plant)
'circumnavigator on staff' is the wordplay.
'circumnavigator' becomes 'drake' (I can't explain this - if you can you should give a lot more credence to this answer).
'on' is a charade indicator (letters next to each other).
'staff' becomes 'man' (manning is a kind of staffing).
'drake' put after 'man' is 'MANDRAKE'.
'discovers magical' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for mandrake that I've seen before include "Naked arm (anag) - narcotic plant" , "Poisonous plant once thought to have magical powers" , "Eurasian plant with purplish flowers" , "A plant; mean, dark (anag.)" , "Root used in medicine" .)